Development and testing of projectiles and vehicles such as anti-aircraft and other missiles is often a lengthy and expensive process. As technological innovations cause onboard surveillance, guidance, and detonation equipment to become increasingly sophisticated, per unit costs and development periods of missiles typically increase. The increased sophistication and cost also frequently expand the mission profiles of the missiles, adding to the number and types of flight scenarios necessarily deemed to be within their performance characteristics. Similarly, advances in both active and passive electronic countermeasures ("ECM") and speed and maneuverability of targets multiply the performance environments for which the missiles must be designed.
Firing a missile at a target ("a live firing") and evaluating telemetry data from the missile (and perhaps from the target as well) present one means by which missile performance characteristics may be tested. As is widely known, however, such live firings are comparatively expensive, requiring extensive pre-flight planning and expending both a missile and a target (if the mission is successful) for each firing. Moreover, only one of many flight scenarios can be tested for each missile firing. Consequently, computer simulations usually are developed in order to generate the bulk of the missile performance information. These simulations rely on mathematical models of, for example, the guidance and surveillance operations of each missile and its associated radars, the known radiation and flight performance characteristics of each missile and target, ECM environments, and atmospheric conditions to emulate live firings. Because models may be developed for virtually every flight scenario for which the missile must be designed and neither actual missiles nor targets are expended, computer simulations provide means by which relatively cost-efficient performance data may be derived.
Although computer simulations in many cases provide reliable information concerning missile characteristics, modelling errors and assumptions concerning critical missile parameters may decrease the overall accuracy or verifiability of the results obtained. To counter this problem, alternative simulations have been developed in which the guidance and surveillance systems of actual missiles have been included in the systems. These systems, called "HIL" simulations, replace the mathematical model of the performance hardware (e.g. the missile being evaluated) with the hardware itself. Thus, even though the missile is not "fired," or expended in any way, data concerning missile performance may be obtained using an actual sample of the missile under test.
HIL systems are an economical means of obtaining initial vehicle performance characterizations, optimizing range testing to obtain comprehensive and detailed data, obtaining vehicle preflight nominal performance parameters, and obtaining a more complete understanding of range test results through post-test simulations of actual range conditions. HIL systems also supplement range testing by simulating conditions such as vehicle and target flight envelopes, target emitter characteristics and electromagnetic environments that may not be available in actual range testing. Since the simulations are performed in a secure, shielded facility, the flight scenario and performance data are more secure, unlike test ranges where optical and electronic reconnaissance may be a concern. Additionally, comprehensive sets of flight scenarios, involving hundreds of simulations, may be performed in the same period of time and for the same cost as one or two live tests.
FIG. 1 illustrates a block diagram of a typical HIL system for evaluating the appropriate guidance and surveillance equipment of a missile. Other HIL systems are described in an undated brochure of the U.S. Army Missile Command, Redstone Arsenal, Alabama, entitled "Research, Development, and Engineering Center/Systems Simulation and Development Directorate/Advanced Simulation Center," which brochure is incorporated herein in its entirety by this reference. In addition to missile under test 14, HIL system 10 includes computers 18 and 22 for controlling flight motion and target parameters, respectively, mechanical means 26 for repositioning missile 14 at various intervals, and a signal projection system 30. Digital and analog links 34, 38, 42, 46, and 50 permit communication between computers 18 and 22 and the other system components. Typically, signal projection system 30 comprises a large, wall-mounted antenna array allowing signal propagation into a shielded anechoic chamber 54 on the order of twenty-five hundred square feet. Not only is the typical signal projection system 30 expensive, but its size and shielding requirements make it impractical for placement in the vast majority of existing buildings. The complex radio-frequency switching hardware and software necessary to energize the many feeds in the array of such a conventional HIL system in order to provide adequate target and environment simulation adds further expense, complexity and maintenance requirements.